1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic head for writing data signals according to a heat-assisted magnetic recording technique.
2. Description of the Related Art
In a magnetic disk drive apparatus intended for higher recording density, a thin-film magnetic head within it needs to be further improved in its performance. As such a thin-film magnetic head, a composite-type thin-film magnetic head is widely used, which has a stacked structure of a magnetoresistive (MR) element for reading data signals and an electromagnetic transducer for writing data signals.
Generally, a magnetic recording medium is magnetically discontinuous, in which magnetic microparticles are gathered together. Usually, each of the magnetic microparticles has a single magnetic-domain structure; and in the medium, one record bit consists of a plurality of the magnetic microparticles. Therefore, for improving its recording density, irregularity in the boundary of the record bit is required to be reduced by decreasing the size (volume) of the magnetic microparticle. However, a problem is likely to occur that the decrease in size causes thermal stability of the magnetization of the record bit to be degraded.
As a measure against the thermal stability problem, it may be possible to increase the magnetic anisotropy energy KU of the magnetic microparticles. However, the increase in energy KU causes the increase in coercive force of the magnetic recording medium. Whereas, write field intensity of the thin-film magnetic head is limited by the amount of saturation magnetic flux density of the soft-magnetic pole material of which the magnetic core of the head is formed. Therefore, the head cannot write data to the magnetic recording medium when the coercive force of the medium exceeds the write field limit.
Currently, as a method for solving the thermal stability problem, a heat-assisted magnetic recording technique is proposed, in which a magnetic head writes data to the magnetic recording medium formed of a material with large magnetic anisotropy energy KU, by reducing the coercive force of the medium with heat supplied to the medium just before the write field is applied. The heat-assisted magnetic recording technique has some similarity to a magneto-optic recording technique. However in the heat-assisted magnetic recording technique, the area of applied magnetic field determines spatial resolution of record bits (that is, magnetic-field-dominant technique). Whereas, in the magneto-optic recording technique, the area of emitted light determines spatial resolution of record bits (that is, light-dominant technique).
As proposed heat-assisted magnetic recording techniques, Japanese patent Publication No. 2001-255254A describes a near-field light probe for irradiating light to the recording medium, which has a metal scatterer with strobilus shape formed on a substrate and a dielectric material film formed around the metal scatterer. And Japanese patent Publication No. 10-162444A describes a head with a solid immersion lens provided within a recording and reproducing apparatus. Further, Japanese patent Publication No. 2004-158067A describes a scatterer as a near-field light probe, which is formed in contact with the main magnetic pole of a single-pole-type head for perpendicular magnetic recording in such a way that the irradiated surface of the scatterer is perpendicular to the medium surface. Furthermore, Miyanishi et al. “Near-field Assisted Magnetic Recording” IEEE TRANSACTIONS ON MAGNETICS, Vol. 41, No. 10, p. 2817-2821 (2005) describes a U-shaped near-field light probe formed on a quartz crystal slider.
Further, US Patent Publication No. 2007/0139818 A1 discloses a thin-film magnetic head having an optic fiber as a means for supplying light from an outside light source. And Japanese Patent Publication No. 2008-10093A discloses a thin-film magnetic head in which a light source is provided on the end surface opposite to the medium-opposed surface of a slider substrate; and the light generated from the light source is directed toward the medium-opposed surface by using a changing-light-path element. Further, US Patent Publication No. 2006/0187564 A1 describes a magnetic head in which a laser diode is attached on the element-integration surface of a slider so that light can reach the incident end face of a light waveguide.
As described above, various forms of heat-assisted magnetic recording techniques are proposed. However, the present inventors suggest a heat-assisted magnetic recording head constituted by joining a light source unit provided with a light source to the end surface (back surface) opposite to the medium-opposed surface of a slider provided with a write head element. For example, Japanese Patent Application No. 2008-047268A discloses such a light source unit. The advantages of the above-described heat-assisted magnetic recording head are as follows:
a) The head has an affinity with the conventional manufacturing method of thin-film magnetic heads because the medium-opposed surface and the element-integration surface are perpendicular to each other in the slider.
b) The light source can avoid suffering mechanical shock directly during operation because the light source is provided far from the medium-opposed surface.
c) The light source such as a laser diode and the head elements can be evaluated independently of each other; thus the degradation of manufacturing yield for obtaining the whole head can be avoided. Whereas, in the case that all the light source and head elements are provided within the slider, the manufacturing yield rate for obtaining the whole head is likely to decrease significantly due to the multiplication of the process yield for the light-source and the process yield for the head elements.
d) The head can be manufactured with reduced man-hour and at low cost, because of no need to provide the head with optical components such as a lens or prism which are required to have much high accuracy, or optical elements having a special structure for connecting optical fibers or the like.
However, in the manufacturing process of the heat-assisted magnetic recording head described above, accuracy of the joining position of the light source unit when joining the unit to the back surface of the slider is required to be significantly high. Actually, the present inventors adopt a structure in which a waveguide is provided within the slider for guiding the light generated by the light source to the medium-opposed surface. When joining the light source unit to this slider, the emission center of the light source needs to be fitted to the incident center of the waveguide, which is positioned on the back surface of the slider. This positioning (fitting) corresponds to the alignment of optical axis in two directions (Y-axis and Z-axis directions) in the back surface of the slider, which is considerably difficult to be performed. As a result, a problem that mass-production efficiency of the head is significantly degraded may be likely to occur.
Further, on joining the light source unit to the slider, there is a possibility that, when the light source, for example, a laser diode, contacts with the back surface of the slider, the generated mechanical stress is applied to the laser diode, which may cause the laser diode to be damaged. However, in order to improve the propagation efficiency of the laser light, the emission center of the laser diode needs to be appropriately positioned adjacent to the incident center of the waveguide. Therefore, required is the joining method for appropriately positioning the emission center of the laser diode adjacent to the incident center of the waveguide, under avoiding the excessive mechanical stress applied to the light source.